Motion capture technology is utilized in various fields such as industry and medical field as well as in the entertainment field. For example, in the field of computer animation, it is possible to achieve more natural-looking movement by applying movement of humans acquired through motion capture to a computer graphics character. In the field of manufacture and development of computer graphics images relating to multimedia and entertainment such as movies and games, motion capture may be indispensable technology. In addition, motion capture technology is also actively employed in various fields such as robotics, biomechanics, sports science, and medical field. Motion capture technology may be optical, magnetic, or mechanical etc. Optical motion capture depends on the type of marker and may be classified into passive optical motion capture and active optical motion capture.
With current motion capture technology, optical motion capture is used where a number of cameras are arranged around a subject and the subject is photographed with the number of cameras. Three-dimensional position information is then calculated by synthesizing two-dimensional information obtained from these images. The optical motion capture is commonly used in applications requiring a high degree of precision taking place at high-speed. This is because accuracy is high compared to other methods, the subject is not particularly inconvenienced, and the subject is not subjected to the influence of magnetism, etc.
In optical motion capture, it is common to attach feature points referred to as “markers” to the subject in order to facilitate image processing. Three-dimensional positions for the markers can then be calculated using triangulation theory by collating marker position information obtained from a number of viewpoints. This processing is referred to as three-dimensional reconstruction, and in order to carry this out it is necessary to know the corresponding relationship of markers detected by the number of cameras. After three-dimensional reconstruction, motion of a link mechanism is obtained by mapping three-dimensional position information for the markers to motion of a link mechanism model for a human. This is carried out using usual inverse kinematics calculations and it is necessary to know which part of the subject each detected marker is fixed to. The process for obtaining this information is referred to as “labeling”.
It is therefore the objective of current motion capture methods to model a person's body as mechanisms of rigid links and joints and to measure joint angles. However, detailed data including changes in the shape of a body during motion may be required depending on the application, and the extent of detail of the measured data is one important problem. Making this detailed refers to the measuring of data that is spatially highly dense by increasing the number of measuring points.
Passive optical motion capture employs markers covered with a retroreflective material. The retroreflective material usually has the property of reflecting light in the direction of a light source. It is therefore easy to detect the marker by placing the optical light close to the camera. The marker itself does not generate light and the extent to which the subject is inconvenienced is extremely small. However, three-dimensional reconstruction and labeling are difficult because of the lack of distinction between markers. When the number of markers increases, the amount of processing exponentially increases and the likelihood of erroneous recognition also increases.
On the other hand, with active optical motion capture, the markers themselves are light sources. Three-dimensional reconstruction and labeling can therefore be made straightforward by changing the color and timing of illumination of the markers. However, the extent to which the subject is inconvenienced increases because wires are necessary to supply electrical power to the markers. Further, the number of markers that can be utilized at one time is limited, and measurement of motion of a number of subjects at the same time is difficult.
In this way, with optical motion capture of the related art, it is necessary to increase the number of markers in order to obtain highly detailed data. However, in particular, because of the following reasons, it is difficult to increase the number of markers in optical motion capture methods of the related art.
(1) According to passive optical motion capture of the related art, when markers are arranged in close proximity to each other, the likelihood of errors being made with regards to correlation of the markers between camera images taken from different viewpoints in calculation of three-dimensional positions for the markers increases, and calculation of three-dimensional positions becomes difficult.
(2) According to passive optical motion capture of the related art, the amount of processing increases exponentially when the number of markers is increased.
(3) According to active optical motion capture of the related art, the number of markers is physically restricted.
The following similar technology also exists in addition to motion capture. A stereo vision system automatically extracts feature points from images and performs three-dimensional reconstruction. However, application to calculation of motion is difficult because processing takes substantial time. Further, it is also difficult to obtain the same precision as for motion capture. A three-dimensional scanner for measuring a three-dimensional shape of a physical body by irradiating a subject with a laser pattern etc. and photographing the result with a camera exists as technology for measuring the three-dimensional position of a number of points with a high-degree of precision. However, measurement of a physical body in motion is difficult because irradiation of the whole of the subject with a laser takes a certain period of time. Further, these methods are based on a completely different theory to that of current optical motion capture and their introduction therefore requires replacement of both hardware and software.
It is therefore an object of the present invention to measure data with a high degree of spatial density by increasing the number of measurement points in a motion capture system.
It is therefore a further object of the present invention to suppress the amount of calculation involved when measuring data with a high degree of spatial density by increasing the number of measurement points in a motion capture system.